Hybrid method for the coating of a substrate by a thermal application of the coating

ABSTRACT

In the method for the coating of a substrate ( 3 ), a hybrid coating method is carried out with a thermal process jet ( 2 ) which makes it possible to combine the properties of a thermal spray method with those of a reactive vapour phase deposition. The properties of the process jet are determined by controllable process parameters, in particular by the parameters of pressure, enthalpy, composition of a process gas mixture (G) and composition and form of application of a coating material (M). The coating material is partly or completely evaporated in dependence on the controllable parameters. The phases of the coating material present in vapour form ( 23   b ) and, optionally, in condensed, i.e. solid or liquid form, ( 23   a ) are at least partly deposited on the substrate. The relative proportion of vapour and/or of condensed phase for the coating material ( 23 ) transported in the process jet is determined by a diagnostic measuring method (D). The controllable process parameters are set with respect to desired values using such gained measured data ( 65 ). A regulation (C) for the direct manufacture of the coating, in particular of a multi-layer coating system ( 4 ), is carried out with respect to these desired values, which correspond to a pre-determined vapour proportion or to a proportion of a condensed phase.

[0001] The invention relates to a hybrid method for the coating of asubstrate by a thermal application of the coating in accordance with thepreamble of claim 1 as well as to applications of the method. Thin filmswith specific material structures and with layer thicknesses in therange from 1-800 μm can be produced with the method.

[0002] The substrate is coated in that a coating material is appliedusing a thermal process jet. The process jet forms a space through whichplasma flows and in which the coating material is transported togetherwith a process gas mixture. The plasma is produced by means of anelectrical gas discharge, electromagnetic induction or microwaves. Anadvantageous method in which a particular process jet is produced isdescribed in U.S. Pat. No. 5,853,815. A so-called LPPS thin film(LPPS=low pressure plasma spraying) is applied to the substrate usingthis method.

[0003] A conventional LPPS plasma spraying method is modified in atechnical process manner with the LPPS thin film process. The coatingmaterial is injected into the plasma in powder form and with a deliverygas. A strong spatial expansion of the plasma results in a “defocusing”of the powder jet. The powder is dispersed to form a cloud and is melteddue to a high enthalpy of the plasma and is, optionally, partlyevaporated. The coating material arrives at a widely expanded surface ofthe substrate in a uniform distribution. A thin layer is deposited whoselayer thickness is less than 10 μm and which forms a dense cover thanksto the uniform distribution. A thicker coating with special propertiescan be produced directly by a multiple application of thin layers.

[0004] Such a coating can be used as a functional layer. A functionallayer, which as a rule includes different part layers, can be applied toa base body which forms the substrate. For example, for gas turbines(stationary turbines or aeroplane engines), which are operated at highprocess temperatures, the vanes are coated with a first single layer ormulti-layer part film such that the substrate becomes resistant to hotgas corrosion. A second coating—of ceramic material—applied to the firstpart layer forms a heat insulating layer. A method is described inEP-A-1 260 602 for the production of such a heat insulating layer systemin which a plurality of individual layers (barrier layer, protectivelayer, heat insulating layer and/or smoothing layer) can be applied by achanging setting of controllable process parameters in one workingcycle. The process parameters are the pressure and enthalpy of theplasma, the composition of the process gas and the composition and theform of application of the coating material.

[0005] It is the object of the invention to provide a method for thecoating of a substrate by a thermal application of the coating, inparticular by a combination of thermal spraying and reactive vapourphase deposition, with which a coating can specifically be produced witha specific material structure—both a homogeneous, heterogeneous and amulti-layer coating. This object is satisfied by the method defined inclaim 1.

[0006] In the method for the coating of a substrate, a hybrid coatingmethod is carried out with a thermal process jet which makes it possibleto combine the properties of a thermal spraying method with those of avapour phase deposition. The properties of the process jet are definedby controllable process parameters, in particular by the parameters ofpressure, enthalpy, composition of a process gas mixture and compositionand form of application of a coating material. The coating material ispartly or completely evaporated in dependence on the controllableparameters. The phases of the coating material present in vapour formand, optionally, condensed form, i.e. in solid or liquid form, are atleast partly deposited on the substrate. The relative proportion of thevapour and/or of the condensed phase for the coating materialtransported in the process jet is determined by a diagnostic measuringmethod. The controllable process parameters are set in relation todesired values using measured date gained in this manner. A regulationfor the direct manufacture of the coating, in particular of amulti-layer coating system, is carried out with respect to these desiredvalues, which correspond to a pre-determined vapour proportion or to aproportion of a condensed phase.

[0007] The method in accordance with the invention is a hybrid coatingmethod in which vapour phases and condensed phases of the coatingmaterial are applied. It combines the properties and possibilities of athermal coating method with those of a vapour phase deposition, inparticular of a reactive deposition. The phases in the process jet aremonitored using a measuring apparatus and the hybrid process isregulated via a setting of suitable process parameters. A controlledsetting of the desired layer structure on the substrate is made possibleby the regulation of the state of the coating material in the processjet.

[0008] The dependent claims 2 to 10 relate to advantageous embodimentsof the method in accordance with the invention. Using the method inaccordance with the invention is the subject matter of claims 11 to 13.

[0009] The invention will be described in the following with referenceto the drawing. There is shown:

[0010]FIG. 1 a schematic illustration of a plant with which the methodin accordance with the invention is carried out.

[0011] A thermal coating method is used with the plant shown which isbased, for example, on the LPPS thin film process and in which thecoating material is applied to a surface 30 of a substrate 3. The plantincludes an apparatus 1 in which a process jet 2 is produced using aknown process P from a coating material M, a process gas mixture G andelectrical energy E. The in-feed of these components E, G and M issymbolised by the arrows 11, 12 and 13. The produced process jet 2emerges through a nozzle 10 and transports the coating material M in theform of a powder jet or precursor in which material particles 23 aredispersed in a plasma 22. This transport is symbolised by the arrow 20.The process jet 2 is shown in enlarged form in the right hand half ofFIG. 1. The material particles 23 are powder particles as a rule;however, they can also consist of a liquid or dispersion. The morphologyof a layer system 4 deposited on the substrate 3 depends on processparameters and in particular on the coating material M, on the processenthalpy and on the temperature of the substrate 3.

[0012] The coating material M is advantageously injected into a plasmadefocusing the material jet and is partly or completely melted thereinat a low process pressure which is less than 10,000 Pa. If a plasma witha sufficiently high specific enthalpy is produced, a substantialproportion of the material particles 23 change into the vapour phase. Astructured layer can thus be created which is a part layer 4 b of thelayer system 4. Structured layers can be created which have lamellar,columnar or mixed material structures. The variation of the structuresis substantially influenced and controllable by the coating conditions,in particular by process enthalpy, operating pressure in the coatingchamber and precursor. The layer system 4 in FIG. 1 has a two-layer filmstructure. As a rule, more than two part layers are deposited. A baselayer 4 a of the system layer 4 has a lamellar structure which resultsat a lower enthalpy such as is used in conventional thermal layersprayed layers. In the second part layer 4 b, elongate corpuscles forman anisotropic microstructure. The corpuscles, which are alignedstanding perpendicular to the substrate surface 30, are bounded withrespect to one another by low-material transition regions.

[0013] The process jet 2 has properties which are defined bycontrollable process parameters. Photons 21 are emitted by the plasma 22which allow conclusions on the properties of the process jet 2. Thematerial particles 23 carried along in the process jet 2 are partly orcompletely evaporated in dependence on the controllable parameters. Thematerial particles 23 finally form a condensed phase 23 a, i.e. a phasepresent in solid or liquid form, and a vapour phase 23 b. In accordancewith the invention, the relative proportion of vapour 23 b and/or ofcondensed phase 23 a is determined by a diagnostic measurement process Dusing a device 5.

[0014] The controllable process parameters are set with respect todesired values using the measured data gained by the process D. Thesedesired values correspond to a vapour proportion or to a proportion of acondensed phase which has to be observed for the direct layermanufacture. A regulation C with respect to the desired values iscarried out using a device 6 to which the measured data are transmittedvia a signal lead 65 in order to produce the special layer structurewhich should, for example, be homogeneous or heterogeneous, inparticular multi-layer. The process parameters are set via signal leads61, 62 and 63.

[0015] For the diagnosis of the process jet 2, an optical measuringmethod D is advantageously used in which in particular the vapourproportion is determined by means of a spectroscopic or pyrometricprocess. The proportion of the condensed phase 23 a, which is present inthe form of a plurality of droplets and/or particles, can also bedetermined by means of a scattered light measurement using an auxiliarylight source, in particular a laser. Two or more measuring methods D canalso be combined.

[0016] The form of application in which the coating material M isinjected into the process stream 2 (arrow 13) can be a powder and/or aliquid, in particular a suspension, and/or a gas, in particular agaseous precursor, with optionally different starting materials beingable to be injected simultaneously using a plurality of injectors.

[0017] Metallic and/or non-metallic substances, in particular oxideceramic substances, can be used for the coating material M. The metallicsubstances are pure metals or metallic alloys, in particular materialsfrom the group of MCrAlY alloys, where M=Ni, Co, CoNi or Fe, orintermetallic phases, for example NiAl compounds. The oxide ceramicmaterials are oxides of Zr, Al, Ti, Cr, Ca, Mg, Si, Tl, Y, La, Ce, ScPr, Dy, Gd or combinations of these chemical elements.

[0018] A reactive gas can be fed to the process gas mixture G andincludes, for example, a hydrocarbon compound, oxygen and/or nitrogenand reacts with one part of the coating material M in the process jet 2.The compounds arising, which are in particular oxides, nitrides,borides, silicides, carbides or aluminides, are deposited on thesubstrate 3 with the non-reacted part of the coating material M.

[0019] The forming of the layer structure 4 is influenced by applying anelectrical potential between the burner electrodes and the substrate 3(so-called “biasing”). Either a positive or a negative bias is possible.The formation of the layer structure 4 can be influenced by theformation of a transmitted light arc or by an additional pre-heating ofthe substrate.

[0020] The process jet 2 is a heat source. An additional heat source canbe used. A heat sink can moreover be provided. The temperature of thesubstrate 3 can be controlled or regulated by influencing a heat inputby the heat source or a heat removal by the heat sink. The applicationof the coating material M can thus be carried out at pre-determinedtemperatures matched to the process conditions.

[0021] The substrate material can consist of organic and/or inorganicmaterial and, optionally, be present as a composite material. Thesubstrate 3 can consist at least partly of a metallic material, inparticular of an alloy, and/or of a ceramic material. The substrate 3 isformed, for example, by the base body of a turbine vane. Or it can bepresent as a component of a fuel cell.

[0022] The method in accordance with the invention can be used, forexample, to produce a coating with a very heterogeneous materialstructure. Such a material structure is in particular a mixed structurewhich includes a porous base structure and non-reacted materialparticles embedded therein.

1. A hybrid method for the coating of a substrate (3) by a thermalapplication of the coating using a process jet (2) whose properties aredefined by controllable process parameters, in particular by theparameters of pressure, enthalpy, composition of a process gas mixture(G) and composition as well as form of application of a coating material(M), with the coating material being partly or completely evaporated independence on the controllable parameters and its phases present invapour form (23 b) and, optionally, in condensed, i.e. solid or liquidform (23 a) being at least partly deposited on the substrate,characterised in that the relative proportion of vapour and/or ofcondensed phase for the coating material (23) transported in the processjet is determined by a diagnostic measuring method (D); and in that thecontrollable process parameters are set with respect to desired valuesusing such gained measured data (65), with a regulation (C) beingcarried out with respect to these desired values, which correspond to apre-determined vapour proportion or to a proportion of condensed phase,for the direct manufacture of the coating, in particular of amulti-layer coating system (4).
 2. A method in accordance with claim 1,characterised in that the process jet (2) is a space through whichplasma (22) flows and in which the process gas mixture (G) and thecoating material (M, 23) are transported, with the plasma being producedwith a known process (P), namely by means of electrical gas discharge,electromagnetic induction or microwaves.
 3. A method in accordance withclaim 1, characterised in that an optical measuring process is used forthe diagnosis (D) of the process jet (2) in which in particular thevapour proportion is determined by means of a spectroscopic orpyrometric process and/or the proportion of the condensed phase, whichis present in the form of a plurality of droplets and/or particles, isdetermined by means of a scattered light measurement using an auxiliarylight source, in particular a laser.
 4. A method in accordance withclaim 1, characterised in that the form of application in which thecoating material (M) is injected into the process stream (13) is apowder and/or a liquid, in particular a suspension, and/or a gas, inparticular a gaseous precursor, with, optionally, different startingmaterials being able to be injected simultaneously using a plurality ofinjectors.
 5. A method in accordance with claim 1, characterised in thatmetallic and/or non-metallic, in particular oxide ceramic substances,are used for the coating material (M); in that the metallic substancesare pure metals or metallic alloys, in particular material from thegroup of MCrAlY alloys, where M=Ni, Co, CoNi or Fe, or intermetallicphases, for example NiAl compounds; and in that the oxide ceramicmaterials are oxides of Zr, Al, Ti, Cr, Ca, Mg, Si, Tl, Y, La, Ce, Sc,Pr, Dy, Gd or combinations of these chemical elements.
 6. A method inaccordance with claim 1, characterised in that a reactive gas is fed tothe process gas mixture (G) and includes, for example, a hydrocarboncompound, oxygen and/or nitrogen and reacts with one part of the coatingmaterial (32) in the process jet (2); and in that the compounds created,which are in particular oxides, nitrides, borides, silicides, carbidesor aluminides, are deposited onto the substrate (3) with the non-reactedpart.
 7. A method in accordance with claim 1, characterised in thatcompounds of the type M_(x)O_(y)N_(z) are deposited as the coatingmaterial (23), where M is a metal, in particular Zr, Al, Cr, Ti, Ta orother metals which form a thermodynamically stable compound of thistype.
 8. A method in accordance with claim 1, characterised in that theformation of the layer structure (4) is influenced by application of anelectrical potential between burner electrodes and the substrate (3). 9.A method in accordance with claim 1, characterised in that an additionalheat source and/or a heat sink are used to carry out the application ofthe coating material (M) at pre-determined temperatures matched to theprocess conditions, with the temperature of the substrate (3) beingcontrolled or regulated by influencing of a heat input by the heatsource or of the heat sink.
 10. A method in accordance with claim 1,characterised in that the substrate (3) consists of organic and/orinorganic material and can, optionally, be present as a compositematerial.
 11. Use of the method in accordance with claim 1,characterised in that a coating is produced on a turbine vane or on acomponent of a fuel cell.
 12. Use of the method in accordance with claim1, characterised in that the morphology of the layer system (4)deposited on the substrate (3) at least partly has—dependent on thecoating material (M), on the process pressure and on the temperature ofthe substrate—a material structure (4 a, 4 b) whose character is atleast approximately lamellar, as with conventional thermal spraycoatings, or columnar, as with special heat insulating layers which areproduced by means of deposition of evaporated coating material (23 b).13. Use in accordance with claim 12, characterised in that the materialstructure is very heterogeneous, in particular a mixed structure, whichincludes a porous base structure and non-reacted material particlesembedded therein.